Add docstring inheritance decorator and drop duplicated docstrings.

mojo/devtools/common/devtoolslib/utils.py

+# Copyright 2015 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""Python utils."""
+
+
+def overrides(parent_class):
+  """Inherits the docstring from the method of the same name in the indicated
+  parent class.
+  """
+  def overriding(method):
+    assert(method.__name__ in dir(parent_class))
+    method.__doc__ = getattr(parent_class, method.__name__).__doc__
+    return method
+  return overriding